This invention relates generally to the field of communication systems, and more particularly to a system and method for call transferring in a communication system.
Call transferring is a supplementary feature often supported in communication systems. Call transferring typically allows one subscriber engaging in a telephone call to transfer the other subscriber to a third party. As a particular example, a first subscriber may be talking to a second subscriber. To initiate a call transfer to a third subscriber, the first subscriber puts the second subscriber on hold and calls the third subscriber. In a xe2x80x9cconsultationxe2x80x9d call transfer, the third subscriber answers the call from the first subscriber, and then the first subscriber transfers the second subscriber to the third subscriber. This may allow, for example, the first subscriber to inform the third subscriber that a call is being transferred. In contrast, during a xe2x80x9cblindxe2x80x9d call transfer, the first subscriber calls the third subscriber and then performs the transfer, without waiting for the third subscriber to answer. The third subscriber is xe2x80x9calerting,xe2x80x9d or the third subscriber""s telephone is still ringing, when the first subscriber transfers the call.
Call transferring also typically involves or affects one or more state machines in the communication system. Devices in the system may be associated with a state machine, which describes the state of the associated device. The device may change from one state to another as calls are initiated, received, and terminated. A typical state machine may have, for example, four states. An idle state indicates that the device is not in use but is ready to be used, and a holding state indicates that the device is on hold. An alerting state indicates that the device is being notified of an incoming call or has placed a call, and a connected state indicates that an active call exists involving the device.
Problems may be encountered in performing call transfers when mobile stations, such as wireless telephones, and other types of telephones communicate with one another through packet clients, such as Voice over Internet Protocol (VoIP) clients. One problem involves the production of xe2x80x9cring back tone,xe2x80x9d or the ringing noise that a calling subscriber hears when the subscriber initiates a call. Mobile stations and other telephones typically do not produce ring back tone themselves, relying instead on a central office or equipment at the other end of a phone call to produce the tone. The ring back tone is then communicated back through the system to the mobile station or other telephone. In contrast, packet clients typically generate their own ring back tones, but only when they are in the alerting state. This difference in operation may create problems during a call transfer. For example, a subscriber using a mobile station or other telephone may need to hear ring back tone so the subscriber knows another subscriber""s telephone is ringing. However, the subscriber""s telephone is unable to produce the tone itself, and the packet client serving the subscriber may be in a connected state, which prevents the client from producing the ring back tone.
To provide the ring back tone to the mobile station or other telephone, conventional systems may attempt to establish a connection in the system between subscribers. This would allow ring back tone to be generated at the called subscriber""s end of the phone call and communicated over the connection to the calling subscriber""s telephone. A problem with this approach is that the subscribers may be billed for this connection. System operators typically bill subscribers after a connection is established in the system. Because this approach establishes a connection between the subscribers, the subscribers will be billed even if the called subscriber never answers the telephone. As a result, this approach increases the expense to one or both subscribers.
Another problem with this approach is that it may produce state violations in the state machine of one or more devices in the system. For example, a conventional system may establish a connection between subscribers so that ring back tone can be provided to the calling subscriber. This may cause the called subscriber""s telephone or packet client to enter the connected state, even though the called subscriber may not have answered the telephone yet. If the called subscriber then answers the telephone, a state violation results. The called subscriber""s telephone or packet client would ordinarily enter the connected state after the subscriber answers the phone, but in this case it is already in the connected state. The state violations could have unexpected consequences to billing and other functions in the system.
In addition, conventional call transferring systems may rely on slower mechanisms to perform the call transfers. For example, the International Telecommunications Union-Telecommunications (ITU-T) H.450 call transfer mechanism uses H.245 signaling messages to perform the call transfers. Using the example given above, H.245 messages may be used to create a connection between the second subscriber and the third subscriber during a consultation call transfer. A problem with this approach is that transferring a call using H.245 messages is typically a slow process. Some systems have faster methods for establishing connections, such as the ITU-T H.323 xe2x80x9cFast Connectxe2x80x9d feature, but those systems do not allow the use of H.245 signaling messages. As a result, conventional call transfer mechanisms that rely on H.245 signaling messages cannot take advantage of the increased speed available in some systems.
As a result of any of these or other disadvantages, previous call transferring techniques have been inadequate in many communication systems.
In accordance with the present invention, a system and method for call transferring in a communication system are provided that substantially eliminate or reduce disadvantages and problems associated with conventional systems. In particular, a communication system allows a mobile station to initiate a call transfer and produces ring back tone for the mobile station or other telephonic device without requiring a connection to be established.
According to one embodiment of the present invention, a system for call transferring in a communication system includes a first client operable to communicate with a mobile station and comprising a ring back tone generator operable to produce a ring back tone. The system also includes a second client operable to communicate with a first telephonic device and with the first client, and a third client operable to communicate with a second telephonic device and with the first and second clients. The system further includes a gatekeeper coupled to the clients and operable to establish a first call connection between the mobile station and the first telephonic device. The gatekeeper is also operable to place the first telephonic device on hold, and establish an alerting call connection between the mobile station and the second telephonic device. The gatekeeper is further operable to instruct the first client to produce ring back tone for the mobile station, and to transfer the first telephonic device to the second telephonic device.
In another embodiment of the invention, a method for call transferring in a communication system includes establishing a first call connection between a mobile station and a first telephonic device. The mobile station is operable to communicate with a first client, and the first telephonic device is operable to communicate with a second client. The first client is operable to communicate with the second client. The method also includes placing the first telephonic device on hold, and establishing an alerting call connection between the mobile station and a second telephonic device. The second telephonic device is operable to communicate with a third client, and the third client is operable to communicate with the first and second clients. The method further includes instructing the first client to produce ring back tone for the mobile station, and transferring the first telephonic device to the second telephonic device.
Numerous technical advantages are provided according to various embodiments of the present invention. Particular embodiments of the invention may exhibit none, some, or all of the following advantages. For example, in one embodiment, a system for call transferring is provided. In particular, the system may allow a mobile station to initiate a call transfer. During the call transfer, the system may generate ring back tone and communicate the ring back tone to the mobile station or another telephonic device participating in the transfer without requiring a connection to be established in the system. As a result, the subscribers may be billed less for using the call transfer feature. Because system operators typically begin billing a subscriber when a connection is formed, the lack of a connection may reduce the amount billed to one or more of the subscribers.
Another advantage of at least some embodiments of the invention is that billing may be further reduced for one or more of the subscribers. For example, in a particular embodiment, the mobile stations and other telephonic devices participating in the call transfer communicate with one another through clients, such as Voice over Internet Protocol (VoIP) clients. In this embodiment, fewer or no datagrams containing bearer information, such as voice traffic, are transported between the clients if a subscriber is on hold or hears ring back tone. Because fewer or no datagrams of information are being transported in the system, this reduction in traffic may further reduce the amount billed to one or more of the subscribers.
A further advantage of at least some embodiments of the invention is that it helps to reduce or eliminate the likelihood that a state violation will occur in one or more components of the system. For example, the system may prevent a subscriber""s telephone or packet client from entering the connected state before the subscriber answers an incoming call. Because a state violation is less likely to occur, the system may reduce or eliminate the unexpected consequences that may accompany state violations.
In addition, at least some embodiments of the invention increase the speed at which calls may be transferred. In a particular embodiment, the system may perform consultation or blind call transfers without requiring the use of International Telecommunications Union-Telecommunications (ITU-T) H.245 signaling messages to perform the transfer. Because H.245 messages are not used, faster methods for establishing connections, such as the ITU-T H.323 xe2x80x9cFast Connectxe2x80x9d feature, can be used during the call transfer. This helps to increase the speed of the call transfers.
Other technical advantages are readily apparent to one of skill in the art from the attached figures, description, and claims.